The present invention relates to nozzles for hot runner systems of plastic injection molds, and in particular, to such nozzles equipped with dynamic seals.
Multi-cavity molds use manifolds to transfer molten plastic from a central feeding point, connected to the sprue bar of the injection machine, to a plurality of injection points leading to the molding cavities. A common problem of hot runner systems is the difficulty to control the thermal expansion of the manifold while maintaining effective sealing between nozzles and manifold. Typical challenges may be: excessive thermal expansion of the components, which may cause failure due to pressures, component fatigue, and wear; insufficient thermal expansion, which may cause uneven or minimal contact between mold components, resulting in plastic leaks; or, in the style of nozzles directly screwed into the manifold, excessive lateral expansion of the manifold, causing lateral deflection of the nozzles.
Previous designs depend on the axial thermal expansion of components to create the seal required to prevent plastic leakage. Thus, if the injection process is started before the system reaches full operating temperature, or if a nozzle heater burns out, the system is likely to leak, as the “cold gaps” are not fully closed. A solution is desired, allowing lateral thermal expansion of the manifold while eliminating lateral deflection of the nozzles, and providing improved axial sealing between the nozzles and the manifold without relying solely on the thermal expansion of the components to achieve such sealing.